Influence of temperature on the physical properties of TEOS silica xerogels

Abstract

In the present paper, the experimental results on the influence of temperature on the physical properties such as bulk density, percentage of porosity, percentage of volume shrinkage and weight loss of silica xerogels, are reported. The xerogels have been prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) using a new catalyst (citric acid) followed by drying at ambient temperatures (<90°C) and atmospheric pressure. The lowest density silica xerogels obtained were of the order of 0.22×10 3 kg m −3. The xerogels were then heated in air at different temperatures ranging from room temperature (25°C) to 1200°C with a controlled heating rate of 1.5°C min −1. It has been found that highly transparent (≈90 %), monolithic, pure and densified (2.2×10 3 kg m −3) silica glasses were obtained at a temperature as low as 980°C when compared to conventional melting of silica glasses (≈2000°C). The experimental results have been discussed by taking into account the processing conditions and related chemical changes. Besides the porosity and density measurements, the gels and glasses were also characterised by infrared (IR) spectroscopy and scanning electron microscopy (SEM).